You need to watch and see who is making the report.
If it is the watch crew - target is in sight.
If it the hydro - target is up to 25km away.
If its the radio man - target can be very far away.
Tip for radio contact: (sorry to realism players
)
lets say you are in the north atlantic and you receive a radio contact.
Think - where is this target going (either west or east)
Guess its av speed at 7knots and plot an intercept cource (50/50 chance you go the correct way)
As you head to intercept, bring up the stop watch and set TC to 128.
Keep an eye on the second hand of the watch.
When it stutters (game is loading something) it will be a contact.
The game will load a unit when it is 30km away from you.
This is good as this is also the range of your hydro.
Dive to 25m - go all stop - listen for contact.
Now you can use hydro info to get close and attack.